In Iran, most households rely on natural gas for their heating and hot water. But amid a cold snap and Gas Shortages, the population has been paralysed by sub-zero temperatures in many regions around the country. These gas shortages have not only led to widespread power cuts, but also severe air pollution from burning low-grade heavy fuel oil, known as mazut, to make up the difference. Despite denials from authorities, the FRANCE 24 Observers team found evidence that this fuel oil is partially responsible for the “unbreathable” air in some Iranian cities.